Method for examining metal for subsurface defects



Oct. 21, 1941. c. McNU TT 2,260,186

METHOD FOR EXAMINING METAL FOR SUBSURFACE DEFECTS Filed May 20, 1938 2 Sheets-Sheet l I NVENTOR LOUIS C. McNUTT Oct. 21, 1941. c, McNUTT METHOD FOR EXAMINING METAL FOR SUBSURFACE DEFECTS Filed May 20, 1938 2 Sheets-Sheet 2 a Hm W.A LU 9 m Patented Oct. 21, 1941 METHOD FOR EXAMINING METAL FOR SUBSUBFACE DEFECTS Louis C. McNutt, Scotch Plains, N. J., assignor to M. W. Kellogg 00., New York, N. Y., a corporalion of Delaware Application May 20, 1938, Serial No. 209,153

3 Claims.

This invention relates to the inspection of metal for the purpose of determining sub-surface defects.

The sub-surface character of the metal empliyed in the fabrication of apparatus, such as the pressure vessels of the petroleum refining, chemical and similar arts, designed to withstand severe service conditions, is highly important. This is especially true of composite metal, 1. e., metal that includes a base such as steel to which is united a comparatively thin protective lining of alloy of special properties. The bond between the alloy and the base is seldom perfect and it is not unusual to find areas of substantial size in an apparently perfect plate, or sheet, at which poor that it may fail in the intended service.

It is not possible to determine, by examination of test pieces, the existence of the unbonded areas in composite metal or the existence of subsurface defects such as laminations, slag and impurity inclusions, gas pockets, etc., in unlined metal. Satisfactory results can only be obtained by an examination of the whole met-a1 body. The prior art does not disclose a simple and inexpensive method for effecting such an. examination.

It is an object of this invention to provide a method for inspecting bodies to determine the existence of sub-surface defects, which method is characterized by its simplicity, efficiency and low cost of operation.

It is also an object of this invention to provide a method for inspecting metal bodies to determine the existence of subscriber defects, which method produces a permanent record of the out- 'line and location of the sub-surface defect on the surface of the body.

The further objects and advantages of the invention willbe better appreciated from a consideration of the following description taken with the accompanying drawings, in which Fig. 1 is a side elevation of a present preferred form of novel apparatus for practicing the method of this invention, and

Fig. 2 is a plan view, with a portion broken out, of the apparatus of Fig. 1.

there is either no bond at all or the bond is so Metal whether in the cast or worked condition, is seldom free from sub-surface defects. This is true of composite metal, 1. e., metal that generally is made up of a steel base to which is united a comparatively thin coating of alloy of special properties, as areas will appear in which there is either no bond at all between the steel base and the alloy coating or the bondis of imperfect character.

It becomes necessary, as for instance, when composite metal is used as the material for pressure vessels, such as the pressure vessels of the petroleum refining, chemical and similar processing arts, that in use are subjected to extreme temperature and pressure conditions, to determine the sub-surface character of the metal so that it may be classified as acceptable or not acceptable for the service. It also becomes necessary, as for instance in the circumstances just above alluded to, to locate sub-surface defects so that these may be removed and the metal repaired.

The novel method of this invention is a complete solution of the inspection problem since it not only makes it possible to determine the existence of sub-surface defects but leaves a permanent record of their location and outline on the surface of the metal. Furthermore, the novel method is a simple one and can be carried out quickly and easily with a minimum of apparatus.

In the present preferred manner of practicing the novel method a source of heat is progressed at a uniform rate over the surface of the metal body to be inspected so that each increment of the surface has applied to it a like quantity of heat at a like temperature' If the body of metal is of homogeneous character each increment of the heated surface will attain the same maximum temperature, If, however, the body is not homogeneous but includes sub-surface defects, as for instance, in composite metal, areas in the zone of union between the alloy covering and the steel base in which the bond is non-existent or is imperfect, the heat transfer rate through these areas is less than through the remainder of the zone of union so that the surface of the metal body overlying these areas attains a higher temperature than the rest of the surface.

This difference of temperature, and hence the existence of sub-surface defects may be indicated in various ways.

- bus, for instance, a plurality of spaced temperature responsive devices, positioned across the heated band; may be progressed with the source of heat, but in back of it. The devices may serve to merely indicate temperature, in which case an operator will mark the high temperature areas, or the devices may be of the recording type so that 1 they will automatically provide a permanent record. At present, I prefer to produce a permanent record on the surface, over whic the source of heat is progressed, of the locati as well as the outline of the sub-surface imperfections.

I accomplish this desirable result byg'employing a heat source which is capable of supplying large by sand blasting. 1 flame is used I have also found it desirable at 1 times to'preheat-the whole plate lightly to remove all moisture from the. surface as at times I water will produce stains which may be confused with the spots indicating imperfections.

quantities of heat at extremely high temperatures and progress the source over the surface to be examined at such a rate that the areas thereof over imperfections of, or greater than, a predetermined minimum area and above a predetermined depth of the metal, are heated to a high enough temperature to produce a permanent and char acteristic; discoloration upon cooling to ordinary temperature. The heat'source may be anoxygen-hydrocarbon flame, an oxygen-hydrogen flame, an electrical resistance, an electric arc discharge between substantially non-consumable,

electrodes, etc.\ At present, I prefer to employ a flame and particularly an oxygen-acetylene flame. To render the method more practical it is preferable to employ a plurality of sources at onetime, the sources being properly spaced to uniformly heat a comparatively wide band of the surface, as wide as several feet or more depending on the areas above the imperfections may be heated to a dull red heat, or higher, without, raising the temperature of the metal of the rest of the surface to temperatures sufficiently high to materially affect its properties and characteristics. Thus, heat'treated metal may be inspected without materially affecting the properties developed by the heat treatment.

Upon cooling, the areas above the imperfections retain a color, usually blue, due to the film of oxide formed thereon. From numerous tests I have found that the colored areas are immediately above the imperfections and, furthermore, that they have substantially the identical pattern. The oxide coloring is a permanent record of the defects and may be used for comparison against a standard and, furthermore, is

' a great help in repairing the metal body.

To assure a true record it is advisable to remove all scale and other foreign matter from g the surface of the body before the heat source is passedover it. This can be conveniently done When the oxygen-acetylene The method maybe employed inthe determination of sub-surface imperfectionslocated at 3 various distances below the surface. By choosing a heatsource of proper capacity and intensity g and progressing the source over. the surface at the" proper rate, imperfections near the surface 1 only, as little as a few hundredths of an inch, 1 willbe indicated, or all imperfections from adjacent the surface to a depth of one-half inch or v i more will be indicated. The limit of penetration 3 cannot be accurately expressed as it depends on lnany factors such as the heat'capacity of the 1 metal, the heat transfer rate, the amount of heat that can be supplied. etc. and can' best be deter-" mined in each case by experiment.

a predetermined depth. After the source is chosen that 'will give the proper penetration the size imperfections that it will indicate will be determined by the rate at which the source is progressed over the work. Thus, one rate will indicate all imperfections in the depth examined while a faster rate will only indicate the larger imperfections.

In the inspection of composite metal, having an alloy lining of 64, of an inch in thickness I have been able with one speed of travel of the heat source to indicate all imperfections as small as 16 inch in diameter, and less, to a depth of A; of an inch and by increasing the speed of travel of the" heat source over the surface I have been able to indicate to the same depth only those imperfectionshaving an average diameter of inch or more.

Further details 'of the novel method will be set forth in the description of the apparatus,

- illustrated in the accompanying drawings, which I method.

is especially suited' for carrying out the novel The apparatus includes a metal frame I0, made -'up of side pieces II and I2, end piece I3, and

a platform I4. The parts of the frame may be 'made of steel plate and joined togetherin any suitable way, as. by welding.

A shaft I5 is supported in bearings carried by pieces and I2 adjacent end piece I3. One

end of shaft I5 is connected to a speed indicat-' ing device I6 which is preferably arranged to indicate speed of travel in convenient unitsas, for instance, feet per minute.

On shaft I5 is fastened a traction wheel II which serves to move the vehicle along 'itspath.

Wheel IT is provided with a periphery of rubber or other non-skid material I8 to prevent slippage of the wheel relative to the, metal body so that a uniform rate of travel may be obtained and accurately indicated at device I6. On shaft I5 'adjacentside piece II is mounted a gear I9 that forms part of the speed reducing gear train that is connected to the shaft of variable speed motor 2|. Gear I9 is mounted for free rotation on shaft I5 and has attached thereto one half of jaw clutch 22. The other half of jaw clutch 22 is splined on shaft |5.- A pin 23, mounted eccentrically on rod 24 that extends through end piece l3, projects into a groove 25 in the splined half of jaw clutch 22. By rotating rod 24,,through handle 26, the halves of jaw clutch 22 may be brought into and out of engagement. Thus, by-

' opening the halves ofjaw-clutch 22 wheel II The inethod has a further flexibility in that it that occur between the surface and rent for the energization may be madev to rotate independently of motor 2| and the apparatus may be quickly pushed about at will by means of handle 21 that isattached to platform I4.

Motor 2| is bolted to a plate 28, which in turn is welded to standards 29 that are bolted to platform I4. Motor 2| includes. a speed changing control 30 by means of which the speed of rotation of motor 2| and consequently the speed'of rotation of wheel I! may be varied at will. Curof motor 2| is supplied through cable 3 {Cable 3| passes through a control box 32 and a switch of the usual construction, not shown. The control switch for cable 3| is opened and closed by themanipulation of handle 33." Handle 33 also operates valves hereinafter to be referred to.

A pair of shafts 34 aresupported for rotation in platform I4 adjacent the forward end of frame I0. To the lower end of each of shafts 34 is fastened an axle 35 upon which a guide wheel 36 is mounted. Guide wheels 36 are each provided with a hardened and sharpened periphery to enable them to bite into the plate over which the apparatus is progressed to facilitate the steering of the apparatus. Shafts 34 are connected together by means of levers 31, 38 and 39 so that a rotary movement of one shaft 34 produces a like rotary movement of the other shaft 34. At the upper end of one of shafts 34 is carried a worm wheel 40 that engages a worm 4| carried by shaft 42. Shaft 42 terminates in a wheel 43 that is provided with a handle 44. By rotating shaft 42 wheels 36 are oriented as desired to steer the apparatus.

A shaft 45 passes through side pieces II and [2 adjacent the forward end of frame l0. Shaft 45 is held against axial movement by set collars 46. On each end of shaft 45 is mounted a bearing 41 that is held -against axial movement by set collars 48. Crosswise to bearing 41 is attached a bearing 49 which supports shaft 50 for rotation.

therein. Shaft 50 is held against axial movement by set collars Each of shafts 50 support a torch member 52. Torch members 52 are also each supported by a pair of casters 53 equi-spaced from shaft 50. By reason of the arrangement just described each of torch members 52 is free to move as required to maintain a predetermined position when irregularities are encountered on the metal surface.

Each torch member 52 includes a plurality of .flame tips 54 that communicate to a central bore.

Tips 54 are so mounted and spaced that a flame of substantially uniform intensity is produced across their full extent. Each torch member 52 has screwed into it, in communication with the central bore, a mixing chamber 55 provided with a Y-shaped top. One branch of the Y is connected through a flexible hose to a valve 56, the other branch is similarly connected to valve 51.

Valves 56 are on manifold 58 and valves 51 on manifold 59. Manifold 58 connectswith line 60 through a valve located in central box 32 and manifold 59 connects with line 6| through a valve also located in control box 32. The valves just mentioned, and the electrical switch previously mentioned are so arranged that by throwing handle 33 in one direction the valves will be opened and the switch closed and by throwing handle 33 in the opposite direction the valves will be closed and the switch opened. By means of this arrangement the flames cannot be ignited without simultaneously initiating the progression of the apparatus over the work, nor can the progression of the apparatus be stopped with-' out simultaneously shutting off the flames. Thus,

the apparatus will always be in motion when the,

flames are burning so that no damage can be done to the metal inspected by reason of an overlong contact with the high intensity flames.

The free end of pipe 62 terminates in a small burner tip 64 that serves as a pilot flame for the ignition of the flames of torch members 52. A pressure gage 63 is carried by pipe 62. A pipe 65, carrying a pressure gage 66, is also tapped into line 6|.

While, as stated, the flames may be oxygenhydrogen or oxygen-hydrocarbon flames I, at present, prefer to employ oxygen-acetylene flames. The acetylene is led from a suitable source, such as the usual pressure cylinder through a flexible line to line 60 and the oxygen is led from a suitable source, also, the usual pressure cylinder through a flexible line to line 6!.

I claim:

1. The method of examining metal bodies for sub-surface defects which comprises progressing a high intensity heat source at a substantially uniform rate over the surface of a metal body to heat the portions of said surface overlying sound metal to a substantially uniform temperature and portions of said surface overlying defects to temperatures higher than said uniform temperature, the intensity of said source and the rate of travel being such that said portions overlying defects are heated high enough to color. 1

2. The method of examining metal bodies for sub-surface defects which comprises progressing -a high intensity heat source at a substantially source to heat portions overlying defects of greater than a predetermined minimum area high enough to-color.

3. The method of examining metal bodies for sub-surface defects which comprises removing scale and other discoloring material from the surface of a metal body, progressing a high intensity heat source at a substantially uniform rate over said surface to heat portions of said surface overlying sound metal to a substantially uniform temperature and portions of said surface overlying defects to temperatures higher than said uniform temperature, the intensity of said source and the rate of travel being such that said portions of Quid surface overlying defects are heated to temperatures high enough to produce a coloring thereon different from that of said portions overlying sound metal upon cooling to ordinary temperatures. 

